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Shingles antiviral timing — GPhC CRA MCQ

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HardInfectionsShingles antiviral timingGPhC CRA

A patient taking dimethyl fumarate for multiple sclerosis has a lymphocyte count of 0.9 × 10⁹/L and new progressive clumsiness, cognitive slowing and visual disturbance. Their next routine blood count is booked in 6 months. What is the most appropriate action?

Educational content. Not a substitute for clinical judgement or local policy.

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Correct answer: D — Stop dimethyl fumarate and urgently investigate possible PML

Explanation lettering: C = shown as B · D = shown as C · E = shown as D · B = shown as E

A is wrong: lymphocytes should be checked at least every 3 months and mild lymphopenia is now a PML risk factor. B misses a potentially life-threatening neurological diagnosis. C is an unvalidated dose strategy and delays investigation. D treats 0.8 × 10⁹/L as an absolute safety threshold when cases have occurred with mild lymphopenia. E is correct: new neurological features require immediate discontinuation and urgent PML assessment.

Reference: MHRA: Dimethyl fumarate—PML associated with mild lymphopenia. https://www.gov.uk/drug-safety-update/dimethyl-fumarate-tecfidera-updated-advice-on-the-risk-of-progressive-multifocal-leukoencephalopathy-pml-associated-with-mild-lymphopenia